"A Korean Air Boeing 747-400, registration HL7601 performing freight flight KE-9560 from Chicago O'Hare,IL (USA) to Brussels (Belgium) with 390 cows travelling on the main deck, was enroute at FL340 over the Irish Sea when the crew received an aft main deck fire warning. A crew member left the cockpit to check the main deck and saw no signs of fire or smoke. Although the crew suspected the indication was false probably caused by the presence of the cows, they decided to carry out the relevant checklist procedures, donned their oxygen masks, initiated a controlled cabin depressurization and performed an emergency descent. The aircraft diverted to London Heathrow,EN (UK) for a safe landing, attending emergency services found no trace of fire or smoke.

The AAIB stated in their bulletin the crew believed "the presence of the cattle led to higher than normal levels of humidity and that this was the cause of the warning."

The bulletin did not state on the fate of the cows.

The airline reported none of the cows suffered from hypoxia during the emergency descent, all of them reached London in good condition."